The objective of this Master’s project was to study the petrography, mineralogy and geochemistry of the Iivaara alkaline intrusion, paying a particular attention to the occurrence of apatite in the intrusion. One of the goals was also to present new information gained from two drill holes drilled in 2012 by the Geological Survey of Finland (GTK). GTK acquired the material from the area during the years 2011–2013; last of them in connection of the Critical Minerals Project. Polished thin sections of outcrop samples and drill core samples were studied using a petrographical microscope and electron microscope. Major element and trace element whole-rock data, determined employing the XRF and ICP-MS methods, were provided by the GTK.
The Iivaara alkaline-intrusion is situated in Kuusamo, eastern Finland, at the SW margin of the Kola Alkaline Province. It was formed approximately at 373–363 Ma, representing a late phase in the magmatism of the province. The intrusion covers an area of 8.8 km², has an ellipsoidal form and is composed mostly of ijolites. Minor rock types include melteigites and urtites occurring mostly in the marginal parts of the intrusion, urtites in the northern part of the intrusion and on top of the Iivaara Mountain, and melilite-bearing rocks in the center of the intrusion. There is an approximately 50- to 700-m-wide fenite zone around the intrusion. In the outcrops, the texture of the ijolite series rocks is heterogeneous, with a network, in which the proportions of nepheline and pyroxene vary. The rocks are mainly metaluminous with minor peralkaline rocks, which are miaskitic. The level of rare earth elements (REE) is low and this also applies to the U and Th contents of the ijolite series, being beneficial for potential exploitation of apatite.
Phosphorus is incorporated in hydroxyl apatite and fluorapatite. Apatite occurs at mineral boundaries sometimes forming a network or as grain clusters. It may also form veins together with biotite. The highest apatite contents are found in pyroxene-rich rocks, such as melteigites and pyroxenites. Also apatite-rich ijolites occur. Fenites have sporadic high contents of P2O5 but generally, the concentrations are as low as in urtites. In outcrop samples, the average P₂O₅ contents are: 1.22 wt.% in urtites, 1.79 wt.% in ijolites, 2.18 wt.% in melteigites, and 1.12 wt.% in fenites. The highest P₂O₅ content, 13.0 wt.%, was measured for an apatite ijolite sample.
Based on whole-rock analyses and thin sections, the variation of mineral compositions in drill cores is roughly similar to outcrops. The magnetite contents in the drill cores are higher than those in outcrop samples, especially in drill core R2. The average apatite content of drill core R1 is higher than in the outcrop samples. The minimum and maximum P₂O₅ concentrations in the more felsic drill core R1 are 1.22 wt.% and 10.10 wt.%, respectively, with an average of 3.50 wt.%. The best 32.5 meters of the drill core has an average P₂O₅ content of 5.52 wt.%. The minimum and maximum P₂O₅ contents in the more mafic drill core R2 are 0.18 wt.% and 5.29 wt.%, respectively, with an average of 1.08 wt.%. The landscape values of Iivaara and its belonging to the Natura 2000 conservation areas need to be evaluated if the mineralization proves to be economic in some future.